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PH-EP-2011-212

(Submitted on 20 Dec 2011)

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Abstract

The decay Bs -> J/\psi K+ K- is investigated using 0.16/fb of data collected
with the LHCb detector using 7 TeV pp collisions. Although the J/\psi \phi\
channel is well known, final states at higher K+K- masses have not previously
been studied. In the K+K- mass spectrum we observe a significant signal in the
f'2(1525) region as well as a non-resonant component. After subtracting the
non-resonant component, we find B(Bs->J/\psi f'_2(1525))/B(Bs->J/\psi
\phi)=(26.4 +/- 2.7 +/- 2.4)%.

(a) The $m(K^+K^-)$ distribution for simulated $\overline{B}^0\rightarrow J/\psi \overline{K}_2^*(1430)$ decays where the $\pi^+$ from the $\overline{K}_2^*(1430)$ decay is interpreted as a $K^+$. The histogram shows $m(K^+K^-)$ in the signal region of $\overline{B}_s^0$ mass and the points in the sideband region. The simulation corresponds to approximately 8 fb$^{-1}$ of data. (b) The $m(J/\psi K^+\pi^-)$ distribution for $J/\psi K^+K^-$ data candidates $25-200$ MeV above the $\overline{B}_s^0$ mass, and with $m(K^+K^-)$ within $\pm$300 MeV of 1525 MeV, reinterpreted as $\overline{B}^0\rightarrow J/\psi K^-\pi^+$ events. The fit is to a signal Gaussian whose mass and width are allowed to vary as well as a quadratic background.

Projections of fits to (a) the $\overline{B}_s^0$ candidate mass and (b) the di-kaon mass. The $f'_2$ signal is parameterized by a spin-2 Breit-Wigner function whose width is fixed to 73 MeV (dotted curve). The combinatorial background is shown in the light shaded region, while the darker shaded region shows the non-resonant $J/\psi K^+K^-$ component. The long-dashed (red) line shows the misidentified $\overline{B}^0\rightarrow J/\psi K^-\pi^+$ decays, and the (blue) line the total.

Distribution of $\cos\theta_{J/\psi}$ for $\overline{B}_s^0\rightarrow J/\psi f'_2$ decays. The background and non-resonant $K^+K^-$ components have been subtracted, and the data have been corrected for acceptance. The fit to Eq. 1 is shown by the solid line. Note that for pure S-wave the distribution would be $\sin^2\theta_{J/\psi}$ ($p=0$), shown as the dotted curve, while for pure helicity 1 ($p=1$) the data would be described by the dot-dashed curve.